The present invention relates to a misfire detecting system for an engine, which determines an occurrence of misfire.
Conventionally, vehicles provided with engines generally perform a misfire determination in which a misfire of an engine is detected. For example, JP2014-136989A discloses an art for calculating a rotational fluctuation of an engine by using a crank angle sensor and performing the misfire determination based on the rotational fluctuation. Specifically in such an art, it is determined that the misfire (one of a single misfire, continuous misfires, and intermittent misfires) has occurred if the rotational fluctuation of the engine exceeds a given misfire determination reference value.
Incidentally, an intake air introducing amount (charging amount) into each cylinder tends to slightly vary depending on the shape of an intake manifold, the smoothness of an intake air flow into the cylinder (or, roughness of the intake air flow), etc. Especially in a situation where a density of intake air (intake air density) introduced into the cylinders becomes high, such a variation of the intake air introducing amount among the cylinders becomes large. As a result, the combustion variation among the cylinders may become large and the crank angle may fluctuate greatly. With the art for determining the occurrence of a misfire based on the crank angle as JP2014-136989A described above, there is a possibility that the crank angle fluctuation is falsely determined as a misfire.